1. Field of the Invention
The present invention relates to an apparatus for performing spot welds wherein the apparatus is actuated by a fluid driven cylinder having an external housing that can float with respect to a plurality of pistons contained within the external housing.
2. Description of the Prior Art
The prior art discloses a variety of welding devices that employ a fluid driven cylinder to move electrodes into and out of engagement with a workpiece. In general, most of the prior art welding assembly devices utilize, in conjunction with a single fluid driven cylinder, steel springs in order to balance or equalize the electrodes about the workpiece. Some prior art devices attempt to balance the electrodes about the workpiece by using two fluid driven cylinders to operate the welding gun assembly. Whether one cylinder with springs or two cylinders are used to equalize the gun, most of these prior art devices mount the body of the fluid driven cylinder about a fixed pivot point, while the rod is attached to a movable pivot point. The resulting arrangement causes the body of the cylinder to oscillate through a relatively large angular sector, therefore requiring that the cylinder be mounted a fair distance from the transformer or any other fixture component to permit the cylinder to oscillate substantially without interfering with any other component mounted on the welding gun fixture assembly. In general, most of the prior art devices utilize a fluid driven cylinder in which the external housing is fixed against axial movement. Such devices rely upon internally positioned pistons and attached piston rods to move relative to the fixed position external housing.
The present invention differs from the welding gun that is shown and described in U.S. Pat. No. 3,008,033 entitled "Welding Gun" issued Nov. 7, 1961, to Charles Senn. FIG. 1 of the Senn patent depicts a pair of cylinders, one within the other in telescoped fashion. The external cylinder has an end closure with a threaded extension for securing the welding gun in a fixed position. The internal cylinder houses a fixed position piston with an accompanying fixed position piston rod that is attached to the end closure of the external cylinder. One end closure of the internal cylinder is in the form of an apertured piston that slides on the fixed position piston rod. The other end of the internal cylinder protrudes from the external cylinder and has attached thereto welding electrodes. By regulating the fluid pressure on either side of the apertured sliding piston and the fixed piston, the internal cylinder can be programmed to move toward and away from a workpiece that is to be welded.
The present invention differs from the above described device in that the external housing of the fluid driven cylinder is capable of controlled movement under the influence of internally positioned pistons.
In U.S. Pat. No. 4,137,828 entitled "Welding Gun" issued Feb. 6, 1979, also to Charles Senn, there is shown a welding apparatus capable of delivering a heavy axial load such as that required for welding concrete reinforcing steel. The welding apparatus utilizes inner and outer telescoped cylindrical members. The external housing is fixed against axial movement and contains an internal cylinder to which welding electrodes are attached. The internal cylinder has an apertured end closure that serves as a piston. A piston rod fixed to and cantilevered from the attached end of the external cylinder passes through the apertured end closure of the internal cylinder. The piston rod contains two spaced apart pistons attached thereto. The internal cylinder contains a fixed position bulkhead that is positioned between the pair of spaced apart pistons. The bulkhead has an axially located aperture through which the piston rod can move relative thereto. The internal cylinder is driven from within the external cylinder under the influence of three air chambers to which air pressure is applied simultaneously. The return stroke of the internal cylinder is controlled by the application of air pressure to a fourth pressure chamber.
While the present invention does use the fixed bulkhead concept in one embodiment, there is no telescoping cylinder arrangement nor is the housing containing the pistons of the fluid driven cylinder fixed with respect to the workpiece.
In U.S. Pat. No. 4,684,778 entitled "Resistance Spot Welding Gun and Transformer Assembly" issued Aug. 4, 1987, to Dimitrios G. Cecil, there is shown and described a spot welding assembly that includes a transformer fixed base and a sliding cylinder mounted thereon. As shown in FIG. 5 of this patent, the sliding cylinder has a closed end and a centrally positioned apertured bulkhead therein. A piston rod is trained through an apertured end closure of the sliding cylinder. The piston rod has dual pistons attached thereto that lie in chambers on either side of the bulkhead that is attached to the sliding cylinder. The piston rod extends when air pressure is introduced between the closed end of the sliding cylinder and the piston located immediately adjacent thereto. The piston rod retracts when air pressure is introduced to the chamber between the bulkhead and the aforesaid piston. Thus, there is axial movement of the piston in one direction and a reaction movement of the sliding cylinder in the other direction. Welding electrodes are attached, respectively, to the free end of the piston and a cantilevered U-shaped arm attached to the sliding cylinder. The above described device permits welding electrodes to be biased in opposed directions toward a workpiece.
U.S. Pat. No. 3,732,784 entitled "Sequentially Operated Linear Actuator" issued May 15, 1973, to Robert A. Vogelei, et al depicts an actuator device that employs two cylinder rods that are in axial alignment and protrude from opposite ends of an external cylindrical housing. The external housing is not adapted for the containment of pressure.
What is lacking in the prior art is a pincher welding gun assembly which utilizes a single fluid driven cylinder without springs, yet provides equalization of the electrodes about the workpiece and also restricts movement of the fluid driven cylinder to allow a compact, lightweight design and assembly of a pincher gun welding assembly.